Boiler with combustion air-cooled superheater



Dec. 30, 1952 F. ca. BRlNlG 2,623,507

BOILER WITH COMBUSTION AIR-COOLED SUPERHEZATER Filed June 3, 1946 3 Sheets-Sheet l INVENTOR.

Dec. 30, 1952 F. e. BRINIG 2,623,507

BOILER WITH COMBUSTION AIR-COOLED SUPERHEATER Filed June 5., 1946 3 Sheets-Sheet 2 INVENTOR.

Dec; 30, 1952 F. G. BRlNlG 2,623,507

BOILER WITH COMBUSTION AIR-COOLED SUPERHEATER Filed June 3, 1946 3 Sheets-Sheet 3 INVENTOR.

Patented Dec. 30, 1952 BOILER WITH COMBUSTION AIR-COOLED SUPERHEATER Frank G. Brinig, Erie, Pa., assignor to Erie City Iron Works, Erie, Pa., a corporation of Pennsylvania Application June 3, 1946, Serial No. 673,917

In the past various devices have been used in an attempt to provide a constant temperature of superheat from a steam generating unit. In an ordinary convection superheater with no control the final steam temperature may vary as much as 200 degrees F. at different loads. Most controls in the past have employed metallic'alloy dampers in the hot gas passes of a steam boiler to deflect these gases from the superheating surfaces. These dampers have been a source of trouble. Other types of controls use various de-superheating or condensing arrangements employing water, which are hard to control and uncertain in operation.

My invention employs a new and unique principle using the combustion air as a tempering medium for de-superheating and at the same time preheating the combustion air. Little or no control is required to maintain constant superheat, since the increased combustion air required for increased boiler loads closely matches the increased de-superheating required to maintain constant superheat. By referring to the illustrations, my method of regulation becomes easily understood.

Fig. 1 is an isometric view of the upper part of a steam generator showing the superheat temperature controlling surface.

Fig. 2 is a side sectional view of the steam generator showing the superheater and the superheat temperature control.

Fig. 3 is a section on 3-3 of Fig. 2 showing air passages over the superheat temperature control surfaces.

In operation, steam is liberated in boiler drum I and discharged to the superheater through row of cross over tubes 2 into superheater header 3. This header communicates with a complete row of superheater elements 4 which discharge back into a header 5. Another row of superheater elements 6 re-enters the convection zone from the header 5 and discharges to superheater outlet header 1. The upper ends of elements 4 and 6 are enclosed in a chamber 8 which is equipped with a baffie 9. Air for control is admitted through duct 10, through control dampers II to the passage below the bafiie 9. This air is directed over the heat exchanger surface provided by upper ends of elements 4 and E and flows back through the passage above the baiile 9 to a discharge duct l2 which preferably conducts the heated air to a point where it may be used, for example, to the boiler furnace where it is used in the combustion process. This is particularly advantageous, since the excess superheat occurs 3 Claims. (Cl. 122-479) at heavy loads where the fuel consumption and demand for combustion air is higher. It has been found that very little, if any, control is needed to maintain constant superheat, since the increased combustion air required for increased boiler loads very closely matches the increased de-superheating required to maintain constant superheat. A thermostatic control unit I3 is located in superheater discharge header 1. Upon a change in temperature, this control opens or closes dampers ll (through suitable connections, not shown) to provide a decrease or increase in the final steam temperature.

As an example of operation, assume a steam generator with a maximum capacity of 300,000 lbs. per hour in which it is desired to maintain a constant final steam temperature in header 1 of 800 degrees F. at all loads down to 200,000 lbs. per hour. If the superheater had no control and had sufficient heating surface to produce 800 degrees F. temperature at 300,000, then the uncontrolled temperature at 200,000 lbs. output would be down in the neighborhood of 720 degrees F. Conversely, if enough heating surface is provided in elements 4 and 6 to give a final temperature of 800 degrees F. at 200,000 lbs. per hour, the uncontrolled temperature at 300,000 lbs. per hour would rise to 875 degrees F. In the present arrangement the surplus heat is removed by air. The superheater heating surface is sufficient to produce the desired steam temperature at the minimum control load without forcing air through the heat exchanger chamber 8. Then as the load increases and the final steam temperature rises above the control temperature, thermostat 13 opens damper ll just sulficiently to reduce the final steam temperature to the desired point.

Fig. 2 is arranged so that the gases of combustion from the furnace sweep first over elements 6 and then over elements 4. In other words, two gas passes are employed. It will be understood that these elements might be combined into one large one and placed in one gas passage without altering my idea of control. This is anticipated in some cases.

In Figs. 1, 2 and 3, air is forced through duct l0 past regulating dampers I l and flows horizontally through the lower half of heat exchanger chamber 8 to the opposite side of the superheater. At this point it flows upward and is forced back through the upper half of the chamber and discharges through duct [2. This heated air is used in the combustion process in the main furnace.

The heat exchanging tubes and chamber can be placed at any point between the superheater inlet and outlet headers with equally good tem perature control. Ordinarily it will be placed at some intermediate point to operate with partial superheat in the tubes. Cases will arise when the exchanger may be placed immediately below the inlet header. Other considerations may conceivably make desirable the placing at the discharge of the superheater elements after the steam has received its entire superheating.

The advantages of the control system are obvious. A quick and ready response is providedfor any change in final steam temperature brought about by any cause. Controlling dampers or louvres are placed in a 0001 location elimihating possible heat failure. No condensation is encountered when tempering superheated steam thus preventing the possible plugging of elements with water or chemical deposits. The temperature of the steam in superheater elements never exceeds the safe design point because of equally distributed air flow. All of the superheater surface is used as heat absorption surface at all loads since no by-passing occurs.

While for descriptive purposes the control is shown on a superheater installed in a three drum boiler, it will be clearly understood that it can and Will be used on superheaters installed in other types of boilers.

What I claim as new is:

1. In: a: boiler having a combustion chamber and steam generatingand superheater sections heated thereby, the sections having heating surfaces so related that the uncontrolled superheat varieswith theboiler load, cooling heat exchange surfaces for the superheater outside the path of combustion gases, means circulating a portion of the combustion air over the heat exchange surfaces on its way to the combustion chamber to supply'preheated air to the combustion chamber, and a control varying the quantity of air circulated over and preheated by the heat exchange surfaces to maintain the desired superheat.

2. In a boiler having a combustion chamber and steam generating and superheater sections heated thereby, the sections having heating surfaces so related that the uncontrolled superheat varies with the boiler load, cooling heat exchange surfaces for the superheater outside the path of combustion gases, a duct carryingcombustion air over the heat exchange surface to the combustion chamber for supplying preheated air for the combustion process, and a superheat regulator means controlling the air flow over the heat exchange surfaces to maintain the desired superheat.

3. In a boiler having a combustion chamber and steam generating and superheater sections heated thereby, the sections having heating surfaces so related that the uncontrolled superheat increases with increasing boiler load, cooling heat exchange surfaces outside the path of the combustion gases and in series with the superheater section, and a duct system for conducting boiler combustion air over saidcooling surfaces to supply preheated air to the combustion chamber for the combustion process.

FRANK G. BRINIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 249,502 Carvalho- Nov. 15,1881 1,439,862 Broido Dec. 26, 1922 2,063,441 Kerr Dec. 8, 1936 FOREIGN PATENTS Number Country Date- 2,963 Great Britain Feb; 5, 1902 1317,2 59 Great Britain Aug. 15, 1929 575,509 Great Britain Feb; 21, 1946 612,230 Germany Mar. 28, 1935 

